What is a codeshare flight?

You book a flight with one airline, walk down the jet bridge, and step onto a plane painted in a completely different airline's colors. Nothing has gone wrong. You have just flown a codeshare, one of the most common and most quietly confusing arrangements in air travel. Here is what it actually means, and why airlines are so fond of it.

One flight, two flight numbers

A codeshare is a single physical flight that two or more airlines sell under their own flight numbers. The aircraft, the crew, the route, and the departure time are all exactly the same. The only thing that changes is the label on your ticket. The "code" in codeshare refers to the airline code, the two-letter prefix in front of every flight number.

Two roles are worth knowing:

• Marketing carrier: the airline you booked with, whose flight number is printed on your ticket.
• Operating carrier: the airline that actually owns the plane and flies it.

When these differ, your booking will usually say something like "operated by" followed by the other airline's name. That small line is your heads-up that a codeshare is in play.

Why airlines do it

Codesharing lets an airline sell seats on routes it does not fly itself. A carrier can put its code on a partner's flight and suddenly offer dozens of destinations it has no planes on. This is a big reason the global airline alliances exist. Star Alliance, Oneworld, and SkyTeam are groups of airlines that codeshare heavily with each other so their combined maps look much larger than any one member's.

It also helps them fill seats and feed connecting traffic. If you fly a partner's plane across an ocean and then connect onto their own aircraft, they capture a longer, more valuable journey without owning every leg of it. For the airline, it is more reach and fuller planes at very little extra cost.

What it means at the airport

For the most part, the operating carrier is the one that counts on the day of travel. A few practical things to expect:

• Terminal and check-in: you generally use the operating carrier's counters, and at large airports that can mean a different terminal than the airline on your ticket. Check which airline is flying you before you set off.
• Onboard experience: the seat, the meal, the legroom, the wifi, and the entertainment all belong to the operating carrier. If you booked a premium brand but the flight is operated by a budget partner, the plane will feel like the budget partner's.
• Gate and boarding pass: signage and announcements typically use the operating carrier's name and flight number, so watch for both numbers on the departure boards.

Bags, lounges, and miles

This is where codeshares get fiddly, so it is worth a moment of attention:

• Baggage: the allowance and fees can follow the operating carrier's rules rather than the airline you booked with. On a single ticket your bags are usually checked all the way through, but the size and weight limits may not be what you expected. Confirm before you pack.
• Lounge access: lounge entry generally follows the operating carrier and your status within that alliance, not simply whose website you used.
• Frequent flyer miles: you can usually credit the miles to your preferred program, but earning rates on codeshare and partner flights are often lower than on the operating airline's own tickets. If miles matter to you, read the earning table first.

Does it change your flight time?

Not at all. The trip is the same length no matter whose name is on the outside of the plane, because it is the same plane on the same route. If you want to know how long that flight really takes from gate to gate, the operating carrier's marketing does not decide it, the distance and the aircraft do.

So a codeshare is less mysterious than it looks. One airline sells the ticket, another flies the plane, and both put their number on the same seat. Know which is which, and you will always turn up at the right terminal with the right bag allowance.

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